In the United States and throughout the world, the re-use of hypodermic syringe products that are intended for single use only is instrumental in drug abuse and more particularly, in the transfer of diseases. Intravenous drug users who routinely share and reuse syringes are a high risk group with respect to the AIDS virus. Also, the effects of re-use are a major concern in developing countries where repeated use of syringe products may be responsible for the spread of many diseases.
Many syringes have been designed to remedy this problem. Some of these have required a specific act to destroy the syringe after use either by using a destructive device or by providing the syringe assembly with frangible zones so that the syringe can be rendered inoperable by the application of force. These syringes allow the destruction or defeating of the syringe function through a conscious act by the syringe user. Although many of these devices work quite well, they do require the specific intent of the user followed by the actual act to destroy or render the syringe inoperable. None of these devices is effective with a user having the specific intent to re-use the hypodermic syringe.
Single-use hypodermic syringes that become inoperative or incapable of further use automatically without any additional act on the part of the user have been developed. One such syringe is disclosed in commonly-assigned U.S. Pat. No. 4,961,728, which is hereby incorporated by reference. The syringe disclosed in this patent includes a locking element positioned in the syringe barrel. The locking element includes proximally and outwardly facing barbs that engage the inner surface of the syringe barrel and an inwardly facing driving edge adapted to interact with a plunger rod to move the locking element along the barrel as the plunger rod is advanced during injection. A stopper is provided at the distal end of the plunger rod and is in a slidable, fluid tight engagement with the syringe barrel. The plunger rod includes a ledge positioned at a distance from the proximal side of a support wall that approximates the length of the locking element. The driving edge of the locking element engages the ledge, thereby ensuring that the locking element moves distally with the plunger rod and stopper. Other syringes including similar locking elements and functionality are disclosed in commonly-assigned U.S. Pat. Nos. 5,989,219 and 6,790,197, which are also incorporated herein by reference.
U.S. Pat. Nos. 5,021,047, 5,062,833 and 5,562,623 disclose single-use syringes having plunger rods that have teeth or ridges and locking elements that engage the teeth or ridges. The locking elements of these syringes also include outwardly extending teeth or prongs that engage the inside surface of the syringe barrel. The plunger rods of these syringes can be retracted to draw fluid into the syringe barrel while the locking elements remain stationary. Distal movement of the plunger rods causes the fluid to be expelled, while the locking elements move distally with the plunger rods with the intention of preventing further plunger rod retraction.
Although the prior art provides syringes having locking elements that will automatically lock the plunger rod to help prevent re-use, the use of such syringes has not been adopted on as large of a scale as necessary, especially in afflicted communities with diminished resources or impoverished nations, to satisfactorily aid in the prevention of drug abuse and the spread of disease. The cost of implementing such a product is a driving force in the adoption of such syringes in developing countries and communities or facilities where drug abuse and diseases are prevalent. Further, because of the typical costs associated with existing syringes one is enticed to attempt the re-use of such a device. Accordingly, there is a desire to produce such a syringe that is more cost effective, thus discouraging its attempted re-use and facilitating more widespread use. It is also desirable to produce such a cost effective single-use syringe that is both optimally effective in preventing its re-use and is easy to use. Namely, it is desirable to reduce the cost of materials and manufacture as well as other associated costs without compromising the effectiveness of the syringe. The smaller sized syringe enabled by the present invention is advantageous in providing a syringe that is more cost effective, thus enabling its widespread use in developing countries and communities where re-use of syringe products may be responsible for the spread of many diseases.
A single use syringe in accordance with embodiments of the present invention is ideal for use in facilities or communities participating in immunization programs to stop the spread of disease. The need for a smaller, yet functional device is further driven by the typical size of an immunization dosage. Such immunization and other similar dosage amounts are often very small, and the use of a smaller device results in many benefits, such as less waste of dosage contents, and ease of use in correctly setting smaller doses because of a heightened perception of the set dosage. Still further, as the typical usage of such devices is with young children or infants, a smaller, yet effective functional device, helps to relieve patient anxiety upon seeing the device. A smaller device avoids the levels of patient anxiety associated with seeing a larger device, especially with pediatric patients.
Providing such a device with the advantages discussed above is not without its challenges. For instance, a balance needs to be achieved between the strength and rigidity of syringe components, namely the plunger rod assembly and locking device, that will provide the optimal effectiveness without compromising the ease of use for the user or the desired functionality of the syringe. Maintaining effective functionality with the reduction in size that is possible with the present syringe device introduces a need for additional features not found in the prior art. A frangible feature is desired along the plunger rod that will cause the destruction of the syringe's functionality if an attempt is made to misuse or re-use the syringe. With a reduced size of the plunger rod assembly, known methods of providing such a frangible feature would unsatisfactorily result in a weakened plunger rod susceptible to inadvertent failure. The frangible feature should be provided in a manner that limits the possibility of accidental destruction of the plunger rod assembly during normal use. In particular, the functionality of the used syringe should be destroyed only upon applying excessive rotational or axial force to the syringe plunger in an attempt to disable the plunger locking mechanism and re-use the syringe. Further, because of the overall reduced size of the syringe, the construction of known plunger rod assemblies would result in a syringe unable to administer the plurality of dosage sizes required by vaccinations and other applications, while effectively preventing its re-use.
Therefore, there is a need for providing more cost effective single-use syringes that are still capable of providing a desired functionality during normal use, while effectively preventing their misuse or re-use.